The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Grant No. 9811289 awarded by Ocean Science Division at the National Science Foundation (OCE).
1. Field of the Invention
This invention relates to underwater sound sources and more particularly to underwater sound sources having applications for RAFOS navigation and acoustic telemetry.
2. Description of the Related Art
The deep sound channel or SOFAR channel has been in use since the early 1970""s to study ocean circulation in a number of studies in the Atlantic and Pacific oceans. Early studies used neutrally buoyant floats, so-called SOFAR floats, which were tracked from land-based hydrophones, and later from moored listening stations. With advances in low-power microprocessors, it became possible to miniaturize the electronics considerably, permitting the reversal of the mode of tracking such that the sound sources became stationary, and the receivers the drifters. This step allowed for a considerable reduction in system cost This reversal of acoustics was coined in the acronym RAFOS (SOFAR spelled backwards). As of today RAFOS floats have been used in studies in both hemispheres of the Atlantic and the Pacific, and most recently around South Africa. Although the advances in technology reduced some aspects of the cost of manufacturing RAFOS floats, a continuing need still exists to further reduce the costs associated with the manufacture of an underwater sound source that can not only be used in RAFOS navigation but also acoustic telemetry. The present invention addresses this need.
Broadly, the invention includes an underwater sound source comprising a housing having an inner and outer surface, two apertures and a monopole driver positioned within the housing. The housing is adapted to be flooded with fluid to form a fluid column inside the housing. The underwater sound source resonates when the monopole driver excites the fluid column. In a preferred embodiment, the monopole driver is a spherical monopole and the length of the housing is in the range of between about 1.5 to 2.5 meters, preferably about 2.0 meters. The length of the housing determines the frequency at which the underwater sound source resonates.
In one aspect of the invention, the length of the housing is about 2.0 meters and the underwater sound source resonates at a frequency of about 260 Hz.
In another aspect of the invention, the underwater sound source resonates when excited by the monopole driver at a frequency within the range of between 200 to 1000 Hz, preferably 260 Hz. The frequency at which underwater sound source resonates is determined by the length of the pipe.
In yet another aspect of the invention, the underwater sound source has a spherical piezoelectric monopole suspended within the center of the housing. The underwater sound source resonates at a frequency of 260 Hz when excited by the monopole.
The housing of the underwater sound source can be cylindrical and typically comprises a free-flooded pipe. The pipe can be comprised of metal, such as aluminum, or a polymer, such as polyvinyl chloride. The housing further comprises an electronics module having a power source positioned on the outer surface of the housing. The electronics module communicates with the monopole driver.
In yet another aspect of the invention, the electronics module is positioned above an open end of the pipe.
FIG. 1 is a front sectional perspective view of an embodiment of the invention;
FIG. 2 is a front sectional perspective view of an alternative embodiment of the invention; and
FIG. 3 is a front sectional perspective view of another alternative embodiment of the invention.